1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor substrate to which a single crystal semiconductor layer is fixed with a buffer layer interposed therebetween and a method for manufacturing a semiconductor device.
2. Description of the Related Art
In recent years, integrated circuits using a silicon-on-insulator (SOI) substrate instead of a bulk silicon wafer have been developed. A feature of a thin single crystal silicon layer formed over an insulating layer can be taken advantage of to form a completely electrically isolated semiconductor layer of a transistor in an integrated circuit and to form a completely depleted transistor. Accordingly, a semiconductor integrated circuit having high added values such as high integration, high-speed operation, and low power consumption can be realized.
Known examples of SOI substrates are SIMOX substrates and bonded substrates. For example, an SOI structure of a SIMOX substrate is obtained by implantation of oxygen ions into a single crystal silicon substrate and by heat treatment performed at 1300° C. or higher to form a buried oxide (BOX) layer, whereby a single crystal silicon thin film is formed on the surface.
An SOI structure of bonded substrates is obtained by bonding of two single crystal silicon substrates (a base substrate and a bond substrate) to each other with an oxide film interposed therebetween and by thinning of one of the single crystal silicon substrates (the bond substrate) on a back side (a side which is opposite to a bonding surface), whereby a single crystal silicon thin film is formed. Because it is difficult to form a uniform and thin single crystal silicon thin film through grinding or polishing, a technique employing hydrogen ion implantation, which is called Smart-Cut (registered trademark), has been proposed (see, for example, Reference 1: Japanese Published Patent Application No. H 5-211128).
A summary of a method for manufacturing this SOI substrate is described. By implantation of hydrogen ions into a silicon wafer, an ion implanted layer is formed at a predetermined depth from the surface. Next, a silicon oxide film is formed by oxidation of another silicon wafer which serves as a base substrate. After that, the silicon wafer into which hydrogen ions are implanted and the silicon oxide film on the other silicon wafer are bonded together to bond the two silicon wafers. Then, through heat treatment, cleavage is caused in the silicon wafer using the ion implanted layer as a cleavage plane, thereby forming a substrate in which a thin single crystal silicon layer is bonded to the base substrate.
In addition, a method for forming an SOI substrate in which a single crystal silicon layer is bonded to a glass substrate is known (see, for example, Reference 2: Japanese Published Patent Application No. H11-097379). In Reference 2, a separation plane is mechanically polished to remove a defective layer which is formed through hydrogen ion implantation or a step of several to several tens of nanometers on the separation plane.
Furthermore, the present applicant has disclosed a method for manufacturing a semiconductor device using Smart Cut (registered trademark), in which a substrate having high heat resistance is used as a supporting substrate, in References 3 and 4 and has disclosed a method for manufacturing a semiconductor device using Smart Cut (registered trademark), in which a light transmitting substrate is used as a supporting substrate, in Reference 5 (Reference 3: Japanese Published Patent Application No. H 11-163363, Reference 4: Japanese Published Patent Application No. 2000-012864, and Reference 5: Japanese Published Patent Application No. 2000-150905).